Short of Read-Only Memory, ROM is a storage medium that is used with computer an other electronic devices. As the name indicates, data stored in ROM may only be read. It is either modified with extreme difficulty or not at all. ROM is mostly use for firmware upadates. A simple example of ROM is the cartridge used with video games consoles, which allows one system to run multiple games.
When switched on, the computer is running a small program recorded in ROM, allowing him to:
Identify the installed processor
Check the amount of RAM included and test it
Examine the hard drive and any additional devices
Read the trace (that is the sector of the hard disk) that contains instruction of booting the system
In particular the ROM boot called the basic input/output system (BIOS). It also interface input/output mechanism of the PC and provides other system servecies including keyboard management, disk, printer, communications and data.